Method of casting volatile metals

ABSTRACT

A method of casting of metals wherein the metal is heated under a pressure sufficient to prevent evaporation or disassociation, is transferred to a mold while the pressure is maintained and is finally cooled under the aforementioned pressure. Thereafter, the pressure is reduced to allow removal of the cast article.

Balevski et al.

3,693,698 1*Sept. 26, 1972 METHOD OF CASTING VOLATILE METALS Inventors:

Assignee:

Notice:

Filed:

Appl. No.:

Angel Tontchev Balevski; Ivan Dimov Nikolov, both of Sofia, Bulgarialnstitut p0 metaloznanie i technologia na metalite, Sofia, Bulgaria Theportion of the term of this patent subsequent to Oct. 6, 1987, has beendisclaimed.

March 28, 1969 Foreign Application Priority Data [5 6] References CitedUNITED STATES PATENTS 3,196,501 7/1965 Balevsky et al ..164/1 193,420,291 1/ 1969 Chandley et al ..164/1 19 X 3,380,509 4/1968I-Ientrich et al. ..164/306 X 3,532,154 10/1970 Balevski et a1 ..164/1192,434,775 l/l948 Sosnick ..75/20 FOREIGN PATENTS OR APPLICATIONS 989,3534/1965 Great Britain ..164/312 Primary Examiner-J. Spencer OverholserAssistant Examiner-V. Rising Attorney-Karl F. Ross [57] ABSTRACT Amethod of casting of metals wherein the metal is heated under a pressuresufficient to prevent evaporation or disassociation, is transferred to amold while the pressure is maintained and is finally cooled under theaforementioned pressure. Thereafter, the pressure is reduced to allowremoval of the cast article.

2 Claims, 4 Drawing Figures April 5, 1968 Bulgaria ..9749

164/133, 164/258 Int. Cl. ..B22d 27/14 Field of Search ..164/1 19, 306

PATENTED P I 3.693.698

sum 1 or 2 1 Angel 71 Balevski Ivan D. Niko/0v F 4 INVENTORS'.

BY Russ I Attorney PATENTEDSEP26 I972 SHEEI 2 [IF 2 Angel I Ba/evskiIvan D. Niko/0v INVENTORS.

METHOD OF CASTING VOLATILE METALS The application relates toapplication, Ser. No. 667,409 filed Sept. 13 1967, now US. Pat. No.3,532,154.

The invention relates to a method and an installation for obtainingcastings from materials which evaporate or disassociate intensively atthe temperature at which it is poured in the mold or from materialswhich may contain components which evaporate or dissociate intensivelyat that temperature, or even before this temperature is reached.

It is known that it is possible to obtain alloys as easily meltingcomponents are melted and their hardly melted components are added tomolten material in which they disolve themselves. However, thispossibility is strongly limited because ordinarily, with the increase ofthe concentration of the high melting components, the meltingtemperature of the alloy as a whole also increases. Thus, beforeobtaining the desired composition it is necessary to raise thetemperature to such a degree at which large and noncontrollable lossesof some of the components may take place as they start to evaporateintensively, or, in certain cases, even begin to sublimate. Because ofthis it has been considered impossible to obtain castings out of alloysof easily evaporating components with a considerable content of highmelting components.

With other materials, processed by foundry techniques, difficultiesarise due to their tendency to dissociate slightly before thetemperatures at which they become sufficiently pourable, is reached.Sometimes difficulties arise even in the production of such materials;these difficulties resemble the abovedescribed dificulties with themetal alloys i.e. some of the initial components are disposed todissociation even before reaching the temperature needed for theobtaining of the material for foundry practices by bonding of thesecomponents.

In practice the evaporation or the dissociation is limited to a certainextent by covering the surface of the molten material by a layer of fluxor surface-active protective means. The layer of flux hinders theoutflow of vapors or the disintegrated products of the molten material,but only until the vapor, or the dissociational pressure, reaches theatmospheric pressure. At higher pressure the flux layer breaks throughand in this way loses its protective effect.

The melting of the components inside an autoclave, of course, with theuse of flux, creates the possibility of obtaining the alloy under anincreased pressure, at least equal to or higher than the vapor pressureof the easily evaporating component at the temperature necessary forobtaining of the alloy or, respectively, the dissociation pressure ofthe easily-diassociating material. The autoclave melting however stilldoes not solve the problem for obtaining castings of such material,because when the pressure is lowered the molds are poured at atmosphericpressure, the above-described undesirable effect of evaporation ordissociation of the easily evaporating or easily dissociating componentswill inevitably take place. To enclose in an autoclave the entire systemof melting, the foundry mold and the connection pipes represent only atheoretical possibility for solving this problem, as the realizationwould be an extremely expensive arrangement which in principle would bein a position to make only single castings.

, to the pouring of themolten material into the mold and the removal ofthe pressure after the solidification of the finished casting, in orderto take it out of the mold, also will have as a consequence anevaporation or a dissociation, as well as an eventual boiling of themolten material.

The object of the invention is a method for obtaining castings by whichthe above-described disadvantages are eliminated, i.e., a method forobtaining of castings from materials in an arbitrary interrelationbetween the temperatures of melting, or evaporation or of dissociationof these materials or of their components.

According to the invention, this is achieved by carrying out the entireprocess from the point of heating of the initial solid material orcomponents thereof for melting, or at their combining together, in orderto obtain the cast material, up to the point of the removal of thesolidified castings from the foundry mold under a regulated gaspressure. At that the gas which exerts thepressure, is selectedaccording to its chemical attitude towards the melted components, as themagnitude of the pressure is regulated according to the requirements ofthe individual phases of the process itself, but always remainssufficiently large in order to prevent an evaporation, or adissociation. At that, the pressure continues to act above the moltenmaterial even then, when it ceases to act above the solidified casting.

In applying the method according to the invention it is possible toutilize the gas pressure which is already created in the installationfor the introduction of the molten material into the mold. It issufficient to increase this pressure from the side of the reservoirholding the molten material, or to lower it from the side of the foundrymold, in order to generate a difference of the pressures giving rise toa flow of the molten material towards the foundry mold with velocitydepending on this difference.

Without changing the substance of the method according to the invention,other known methods for introducing of the molten material into thefoundry mold may be used, such as gravitational, by turning theinstallation in such a way so that the molten material pours from thereservoir into the mold, or by means of a piston pressure.

The invention is further clarified by means of the accompanying drawing,in which:

FIG. 1 is a vertical section through an installation for the realizationof the method according to the invention, in which the molten materialis introduced into the mold under the action of a gas pressure;

FIGS. 2 and 3 are vertical sections of an installation actinggravitationally; and

FIG. 4 is a vertical section of an installation with a piston pressure.

The material to be poured, or its components, is placed in the crucible1 which, together with the heating device 2, is closed hermetically inthe chamber 3. The pipe 4 intended for pouring of the molten materialclosed by the device 5 in such manner that with the gradual increase ofthe temperature inside the chamber 3 the pressure in it may be raised byfeeding a cornpressed gas from the reservoir 6 through the valves 7 and8. At the same time the valve 9 is closed, while the valve 12 is opened,so that the chamber 10 is under the atmospheric pressure, which permitsnecessary auxiliary operations using the foundry mold 11.

When the molten material is ready, the chamber 10 and the mould 11 areisolated from the atmosphere by closing the valve 12 and gas is fed tothem from the reservoir 6 through the valve 9. In this way a constantgas pressure is created in the entire system which is sufficiently highin order to prevent evaporation or dissociation of the molten material.The partition 5 may be removed.

Furthermore, by inducing the desired difference of the pressure betweenchamber 3 of the reservoir for the molten material and the chamber 10for the foundry mold, which may expediently be accomplished by means ofan additional increase of the pressure inside the chamber 3, the moltenmaterial rises inside the feeding pipe 4' and fills the mould l1.Immediately after that the pressure inside the chamber 3 and chamber 10equalize anew, for instance by an increase of the pressure inside thechamber 10 up to the pressure inside the chamber 3, at which the moltenmaterial inside the feeding pipe returns into the reservoirl for themolten material. Now the partition 5 may be closed and inside thechamber 10 for the foundry mold, steps may be taken for an acceleratedcooling of the filled mold 11; after the solidification of the castingthe pressure is dropped by closing the valve 9 and opening the valve 12.After this is done the completed casting may be taken out of the mold11. The process is repeated as after replacing ofv the empty mold, thepressure inside the chamber 10 being raised again by opening of thepartition 5 and a new portion of the molten material being forced intodisassociation mold 11.

The process may be carried out in practice without losses due toevaporation or diassociation if the free surface of the molten materialin the reservoir 1 is protected by a layer of expediently selected flux.Inasmuch as the gas pressure inside the chamber 3 is maintained higherthan the vapor pressure, or the dissociational pressure, of any of thecomponents of the founding material, the protective flux layer remainsunbroken and no elimination of vapor or of products of dissociation willtake place. An equivalent embodiment of the installation for therealization of the method may be obtained by a hermetical enclosure ofthe crucible containing the melted founding material. In such a case byanalogous control of the pressure inside the crucible the same processmay be realized, as the heating device and the chamber in which it isplaced, may be left free under atmospheric pressure.

It is evident from FIGS. 2 and 3 that the gravita tionally actinginstallation for the fulfilment of the method according to theinvention, possesses the basic elements of the installation of FIG. 1and retains the technological sequence of the operations, while for thepouring of the molten material into the mold it is necessary that theentire arrangement be revolved from the position shown at FIG. 2 to theposition shown at FIG. 3. The reservoir for the molten material isclosed hermetically so that it is unnecessary for the reservoir,together with the heating device 2, to be enclosed to the chamber as inthe case with the installation shown in FIG. 1. The components of thefounding material placed in the crucible 1 of the installation shown inFIG 2, are heated by means of the heating device 2 and thy are subjectedunder the action of the gas pressure given rise to by the gas reservoir6 on opening of the valves 7, 8 and 9, this pressure being sufficientlylarge so that it does not allow the evaporation or the disassociation ofthe founding material, or any of its components at the temperature whichmust be reached in order to fulfill the pouring of the material. Uponthe attainment of this temperature, the arrangement is revolved to theposition shown at FIG. 3, with the partition 5 kept opened, in order tofill in gravitationally the foundry mould 11 with the molten material.

In completing the casting of the material the partition 5 is closed. Byan expedient forming of the feeding pipe 4 this closing may be doneafter revolving of the arrangement back to the original position (FIG.2) and by closing of the valve 9 and opening of the valve 12, thealready solidified casting may be taken out of the mold 11, which is notunder pressure.

If in the path of the molten material in the feeding pipe 4 is placed adosage cylinder 13 (FIG. 4) with a moving piston 14, then part of themolten material, which has found its way into this cylindrical by theaction of the difference of the gas pressures, may be forced into themold by displacing the piston 14. A dosage cylinder has a predetermineddisplacement per stroke to control material feed. The valve 15 makes itpossible for the pressure behind the piston 14 to equalize with thepressure inside the melting chamber 3 inorder to enable the return ofthe remaining molten material in the feeding pipe back to the reservoir.Upon the completion of the stroke of the piston, atmospheric pressure isestablished inside the chamber 10 by the closing of the valve 9 and byopening of the valve 12. Then the casting may be taken out of the mold11.

Every one of the described installations may be applied for casting ofreaction-active materials, by chosing a neutral, respectively areduction protective gaseous medium.

We claim:

1. A method of casting a volatile or disassociable meltable material ata temperature above its boiling or decomposition point, comprising thesteps of:

a. melting said material in a first chamber and generating a pressuretherein at a superatmospheric level sufficient to prevent volatilizationof the molten material;

b. providing a mold in a second chamber communicating with thefirst-mentioned chamber;

0. mechanically blocking communication between said chambers whileventing said second chamber to the atmosphere during melting of saidmaterial in said first chamber and the buildup of the pressure thereinto said superatmospheric level;

d. disconnecting said second chamber from the atmosphere and raising thepressure therein from a source other than said first chamber to asuperatpreventing superatmospheric pressure above the mospheric levelless than the first-mentioned level molten material in both saidchambers at all times to create a pressure differential between said andthroughout steps and and chambers; g. supplying pressure from anexternal source to said e. thereafter mechanically opening communicatio5 first chamber during step t malmflin the p between said chambers todrive the molten materi- Sure 531d first chamber cqnstam f f i fi tchamber i said Second 2. The method defined m claim 1 wherein saidmolchamber and said mold at least in part under the P mammal Permmed toflow y gravity to Said mold force of said pressure differential; p f.maintaining dissociation and evaporation 10

1. A method of casting a volatile or disassociable meltable material ata temperature above its boiling or decomposition point, comprising thesteps of: a. melting said material in a first chamber and generating apressure therein at a superatmospheric level sufficient to preventvolatilization of the molten material; b. providing a mold in a secondchamber communicating with the first-mentioned chamber; c. mechanicallyblocking communication between said chambers while venting said secondchamber to the atmosphere during melting of said material in said firstchamber and the buildup of the pressure therein to said superatmosphericlevel; d. disconnecting said second chamber from the atmosphere andraising the pressure therein from a source other than said first chamberto a superatmospheric level less than the firstmentioned level to createa pressure differential between said chambers; e. thereaftermechanically opening communication between said chambers to drive themolten material from said first chamber into said second chamber andsaid mold at least in part under the force of said pressuredifferential; f. maintaining dissociation - and evaporation - preventingsuperatmospheric pressure above the molten material in both saidchambers at all times and throughout steps (a) and (e); and g. supplyingpressure from an external source to said first chamber during step (e)to maintain the pressure in said first chamber constant during step (e).2. The method defined in claim 1 wherein said molten material ispermitted to flow by gravity to said mold in step (e).